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Abstract:

The present invention relates to a fluorine-free photoacid generator
(PAG) and a photoresist composition containing the same. The PAG is
characterized by the presence of an onium cationic component and a
fluorine-free fused ring heteroaromatic sulfonate anionic component
containing one or more electron withdrawing substituents. The onium
cationic component of the PAG is preferably a sulfonium or an iodonium
cation. The photoresist composition further contains an acid sensitive
imaging polymer. The photoresist composition is especially useful for
forming material patterns on a semiconductor substrate using 193 nm (ArF)
lithography.

Claims:

1. A fluorine-free photoacid generator, said photoacid generator
comprising an onium cationic component and an anionic component having
one of the following two structures: ##STR00013## wherein: X is
selected from the group consisting of S, O and NR; R is selected from the
group consisting of H; linear, branched, tertiary, or cyclic alkyl;
linear, branched, tertiary or cyclic alkoxyl; unsubstituted and
substituted aromatic groups; and unsubstituted and substituted
heteroaromatic groups; Y is selected from the group consisting of C and
N; each of G1-G5 is selected from the group consisting of R and
an electron withdrawing moiety, provided that when Y is N, G1 is not
present in the structure and at least one of G1-G5 is an
electron withdrawing moiety and; the photacid generator can produce acid
upon exposure to ultraviolet (UV) light.

2. The photoacid generator of claim 1 wherein at least one of
G1-G5 is an electron withdrawing moiety selected from the group
consisting of CN, NO, NO2, Cl, Br, I, SO2Me, and CHO.

3. The photoacid generator of claim 2 wherein at least one of
G1-G5 is selected from the group consisting of CN and NO.sub.2.

4. The photoacid generator of claim 2 wherein at least two of
G1-G5 are electron withdrawing moieties.

5. The photoacid generator of claim 1 wherein said onium cationic
component is selected from the group consisting of sulfonium cations and
iodonium cations.

7. The photoacid generator of claim 6 wherein said onium cationic
component has a structure selected from the group consisting of
##STR00014## wherein each of R1, R2, R3, R4, and
R5 is independently selected from the group consisting of H; linear,
branched, tertiary, or cyclic alkyl; linear, branched, tertiary or cyclic
alkoxyl; unsubstituted and substituted aromatic groups; and unsubstituted
and substituted heteroaromatic groups.

8. A photoresist composition comprising: (a) an acid sensitive imaging
polymer; and (b) a fluorine-free photoacid generator comprising an onium
cationic component and an anionic component having one of the following
two structures: ##STR00015## wherein: X is selected from the group
consisting of S, O and NR; R is selected from the group consisting of H;
linear, branched, tertiary, or cyclic alkyl; linear, branched, tertiary
or cyclic alkoxyl; unsubstituted and substituted aromatic groups; and
unsubstituted and substituted heteroaromatic groups; Y is selected from
the group consisting of C and N; each of G1-G5 is selected from
the group consisting of R and an electron withdrawing moiety, provided
that when Y is N, G1 is not present in the structure and at least
one of G1-G5 is an electron withdrawing moiety; and the
composition is photosensitive.

9. The photoresist composition of claim 8 wherein at least one of
G1-G5 is an electron withdrawing moiety selected from the group
consisting of CN, NO, NO2, Cl, Br, I, SO2Me, and CHO.

10. The photoresist composition of claim 9 wherein at least one of
G1-G5 is selected from the group consisting of CN and NO.sub.2.

11. The photoresist composition of claim 9 wherein at least two of
G1-G5 are electron withdrawing moieties.

12. The photoresist composition of claim 8 wherein said onium cationic
component is selected from the group consisting of sulfonium cations and
iodonium cations.

14. The photoresist composition of claim 13 wherein said onium cationic
component has a structure selected from the group consisting of
##STR00016## wherein each of R1, R2, R3, R4, and
R5 is independently selected from the group consisting of H; linear,
branched, tertiary, or cyclic alkyl; linear, branched, tertiary or cyclic
alkoxyl; unsubstituted and substituted aromatic groups; and unsubstituted
and substituted heteroaromatic groups.

16. The photoresist composition of claim 8 wherein said imaging polymer
has a weight concentration ranging from about 5% to about 20% of the
total weight of said photoresist composition.

17. The photoresist composition of claim 8 wherein said fluorine-free
photoacid generator has a weight concentration ranging from about 0.5% to
about 15% based on the total weight of said imaging polymer.

18-28. (canceled)

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation of and claims priority to
co-pending U.S. patent application Ser. No. 12/692,962, filed Jan. 25,
2010, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention relates to photolithography, and more particularly
to fused ring heteroaromatic photoacid generators which are fluorine-free
and efficiently generate acids upon exposure to UV light. This invention
is also directed to resist compositions containing the inventive
fluorine-free fused ring heteroaromatic photoacid generators and methods
of using the resist compositions in photolithography.

BACKGROUND OF THE INVENTION

[0003] Miniaturized electronic components such as integrated circuits are
typically manufactured using photolithography technology. In a
photolithography process, a photoresist layer is formed on a substrate,
such as a silicon wafer. The substrate is baked to remove any solvent
remained in the photoresist layer. The photoresist is then exposed
through a photomask with a desired pattern to a source of actinic
radiation. The radiation exposure causes a chemical reaction in the
exposed areas of the photoresist and creates a latent image corresponding
to the mask pattern in the photoresist layer. The photoresist is next
developed in a developer solution, usually an aqueous base solution, to
remove either the exposed portions of the photoresist for a positive
photoresist or the unexposed portions of the photoresist for a negative
photoresist. The patterned photoresist can then be used as a mask for
subsequent fabrication processes on the substrate, such as deposition,
etching, or ion implantation processes.

[0004] One type of photoresist employed in the prior art is a chemically
amplified photoresist which uses acid catalysis. Chemically amplified
photoresists have increased sensitivity to exposure energy over
non-chemically amplified photoresists. A chemically amplified photoresist
is especially useful when relatively short wavelength radiation is
employed, such as deep UV radiation (150-315 nm wavelengths) and mid-UV
radiation (350-450 nm wavelengths).

[0005] A typical prior art chemically amplified photoresist, for example,
is formulated by dissolving an acid sensitive base polymer and a
photoacid generator (PAG) in a casting solution. The base polymer in a
chemically amplified positive photoresist typically has acid labile
groups bonded to the polymer backbone. When such a photoresist is exposed
to radiation, the PAG absorbs photons and produces an acid. The photo
generated acid then causes catalytic cleavage of the acid labile groups.
A single acid molecule generated in this manner may be capable of
cleaving multiple acid labile groups on the base polymer. Thus, fewer
photons are needed to render the exposed portion of the photoresist
soluble in the developer solution.

[0006] Because of the relatively low intensity of a 193 nm laser source
and relatively high binding energy of acid labile groups in a 193 nm
photoresist, PAGs which can produce stronger Bronsted acid with high
sensitivity are preferred to realize such a chemical amplification in
commercial 193 nm photolithography. Fluorine-containing PAGs, such as
perfluorooctyl sulfonate (PFOS) and perfluoroalkyl sulfonate (PFAS), are
generally preferred PAGs in 193 nm photoresist system partially because
they result in generation of strong acids.

[0007] In recent years, however, there has been a desire in the
microelectronics industry to eliminate the use of perfluorinated carbons
(PFCs) including PFOS and PFAS due to their detrimental effects on
environment, human and animals. Thus, there is a desire to find
alternative PAGs which can be used without adversely impacting the
performance of lithographic processes. There has also been a desire to
minimize or eliminate fluorine content in photoresist in order to improve
etch resistance and to improve process latitude in high numeric aperture
(NA>0.95) imaging processes. Accordingly, there is a need for new and
improved fluorine-free PAGs and chemically amplified photoresist
compositions that enable the substantial reduction or avoidance of
fluorine content in photoresist compositions.

SUMMARY OF THE INVENTION

[0008] The present invention provides fluorine-free photoacid generators
which are a viable alternative to the PFC-containing photoacid generators
currently used in the industry. This invention also provides photoresist
compositions containing such a fluorine-free photoacid generator that
show excellent optical clarity and thermal stability and have
lithographic performance equal to or better than that of photoresists
having the PFC-containing photoacid generators.

[0009] In one aspect, the present invention relates to a fluorine-free
photoacid generator including an onium cationic component and an anionic
component having one of the following two structures:

##STR00001##

[0010] wherein:

[0011] X is selected from the group consisting of S, O and NR;

[0012] R is selected from the group consisting of H; linear, branched,
tertiary, or cyclic alkyl; linear, branched, tertiary or cyclic alkoxyl;
unsubstituted and substituted aromatic groups; and unsubstituted and
substituted heteroaromatic groups;

[0013] Y is selected from the group consisting of C and N; and

[0014] each of G1-G5 is selected from the group consisting of R
and an electron withdrawing moiety, provided that when Y is N, G1 is
not present in the structure and at least one of G1-G5 is an
electron withdrawing moiety.

[0015] The onium cationic component of the fluorine-free photoacid
generator is preferably selected from the group consisting of sulfonium
cations and iodonium cations. The onium cationic component preferably
includes an aromatic moiety.

[0016] In another aspect, the present invention relates to a photoresist
composition including: [0017] (a) an acid sensitive imaging polymer;
and [0018] (b) a fluorine-free photoacid generator comprising an onium
cationic component and an anionic component having one of the following
two structures:

[0018] ##STR00002## [0019] wherein: [0020] X is selected from the
group consisting of S, O and NR; [0021] R is selected from the group
consisting of H; linear, branched, tertiary, or cyclic alkyl; linear,
branched, tertiary or cyclic alkoxyl; unsubstituted and substituted
aromatic groups; and unsubstituted and substituted heteroaromatic groups;
[0022] Y is selected from the group consisting of C and N; and [0023]
each of G1-G5 is selected from the group consisting of R and an
electron withdrawing moiety, provided that when Y is N, G1 is not
present in the structure and at least one of G1-G5 is an
electron withdrawing moiety.

[0024] The imaging polymer of the photoresist composition preferably has a
lactone moiety. The imaging polymer preferably has a weight concentration
ranging from about 1% to about 30% of the total weight of the photoresist
composition. The fluorine-free photoacid generator preferably has a
weight concentration ranging from about 0.5% to about 20% based on the
total weight of said imaging polymer.

[0025] In still another aspect, the present invention relates to a method
of forming a patterned material feature on a substrate including the
steps of: [0026] (a) providing a material layer on a substrate; [0027]
(b) forming a photoresist layer over the material layer, the photoresist
comprising: [0028] (i) an acid sensitive imaging polymer; and [0029]
(ii) a fluorine-free photoacid generator comprising an onium cationic
component and an anionic component one of the following two structures:

[0029] ##STR00003## [0030] wherein: [0031] X is selected from the
group consisting of S, O and NR; [0032] R is selected from the group
consisting of H; linear, branched, tertiary, or cyclic alkyl; linear,
branched, tertiary or cyclic alkoxyl; unsubstituted and substituted
aromatic groups; and unsubstituted and substituted heteroaromatic groups;
[0033] Y is selected from the group consisting of C and N; and [0034]
each of G1-G5 is selected from the group consisting of R and an
electron withdrawing moiety, provided that when Y is N, G1 is not
present in the structure and at least one of G1-G5 is an
electron withdrawing moiety; [0035] (c) patternwise exposing the
photoresist layer to radiation, thereby creating a pattern of
radiation-exposed regions in the photoresist layer; [0036] (d)
selectively removing portions of the photoresist layer to expose portions
of the material layer; and [0037] (e) etching or ion implanting the
exposed portions of the material layer, thereby forming the patterned
material feature.

[0038] The radiation of the method is preferably provided by an ArF laser.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0039] It will be understood that when an element, such as a layer, is
referred to as being "on" or "over" another element, it can be directly
on the other element or intervening elements may also be present. In
contrast, when an element is referred to as being "directly on" or
"directly over" another element, there are no intervening elements
present.

[0040] The present invention provides a fluorine-free photoacid generator
(PAG) which is a viable alternative to the PFC-containing photoacid
generators currently used in the industry. The fluorine-free PAG is
generally characterized by the presence of an onium cationic component
and an anionic component having one of the following two structures:

##STR00004##

[0041] wherein:

[0042] X is selected from the group consisting of S, O and NR;

[0043] R is selected from the group consisting of H; linear, branched,
tertiary, or cyclic alkyl; linear, branched, tertiary or cyclic alkoxyl;
unsubstituted and substituted aromatic groups; and unsubstituted and
substituted heteroaromatic groups;

[0044] Y is selected from the group consisting of C and N; and

[0045] each of G1-G5 is selected from the group consisting of R
and an electron withdrawing moiety, provided that when Y is N, G1 is
not present in the structure and at least one of G1-G5 is an
electron withdrawing moiety.

[0046] In one embodiment of the present invention, one of G1-G5
is an electron withdrawing moiety. In another embodiment of the present
invention, at least two of G1-G5 are electron withdrawing
moieties. Examples of the electron withdrawing moieties suitable for the
present invention include, but are not limited to, CN, NO, NO2, Cl,
Br, I, SO2Me, and CHO. Preferably, at least one of G1-G5
is CN or NO2.

[0047] The onium cationic component of the fluorine-free PAG is preferably
a sulfonium cation or an iodonium cation. Preferably, the onium cationic
component has an aromatic moiety. The aromatic structure of the cationic
component generally improves the thermal stability of the resulting
fluorine-free PAG. Two preferred cationic component for the present
invention are:

##STR00005##

wherein each of R1, R2, R3, R4, and R5 is
independently selected from the group consisting of H; linear, branched,
tertiary, or cyclic alkyl; linear, branched, tertiary or cyclic alkoxyl;
unsubstituted and substituted aromatic groups; and unsubstituted and
substituted heteroaromatic groups. Examples of a sulfonium cation of the
structure (III) are:

##STR00006##

[0048] An example of an iodonium cation of the structure (IV) is:

##STR00007##

[0049] Examples of the anionic component of structures (I) and (II) are:

##STR00008##

[0050] The invention is not limited to any specific method for
synthesizing the fluorine-free PAGs of the invention. One possible
synthesis route is shown in Scheme 1 below.

##STR00009##

[0051] As shown in Scheme 1, in one embodiment, the synthesis of the
fluorine-free fused-ring heteroaromatic PAGs starts from the nitro
substitution reaction of a fused-ring heteroaromatic sulfonyl chloride,
followed by a one-pot reaction to convert the nitro-substituted
fused-ring heteroaromatic sulfonyl chloride to its corresponding silver
sulfonate. The nitro-substituted fused-ring heteroaromatic sulfonyl
chloride reacts with silver carbonate to afford the silver salt in solid
phase at almost quantitative yield. The resulting silver salt then reacts
with a corresponding sulfonium (or iodonium) source to afford the desired
fluorine-free fused-ring heteroaromatic PAG. The chemical structures of
the resulting fluorine-free fused-ring heteroaromatic PAGs can be
confirmed by their NMR spectra. In the instance of synthesis of the
triphenyl sulfonium mono nitro-benzo[b]thiophene-2-sulfonate (TPSTBNO) as
shown in Scheme 1, the resulting PAG is a mixture of two isomers A and B
with a molar ratio of 65:35.

[0052] The invention also encompasses a photoresist composition containing
the fluorine-free PAGs of the present invention. The photoresist
composition has an acid sensitive imaging polymer and a fluorine-free PAG
having an onium cationic component and an anionic component having one of
the following two structures:

##STR00010##

[0053] wherein:

[0054] X is selected from the group consisting of S, O and NR;

[0055] R is selected from the group consisting of H; linear, branched,
tertiary, or cyclic alkyl; linear, branched, tertiary or cyclic alkoxyl;
unsubstituted and substituted aromatic groups; and unsubstituted and
substituted heteroaromatic groups;

[0056] Y is selected from the group consisting of C and N; and

[0057] each of G1-G5 is selected from the group consisting of R
and an electron withdrawing moiety, provided that when Y is N, G1 is
not present in the structure and at least one of G1-G5 is an
electron withdrawing moiety.

[0058] The imaging polymer is preferably capable of undergoing chemical
transformations upon exposure of the photoresist composition to UV light
whereby a differential in the solubility of the polymer in either the
exposed regions or the unexposed regions is created. The imaging polymer
may be either a positive-tone imaging polymer or a negative-tone imaging
polymer. When the imaging polymer is a positive-tone imaging polymer, it
preferably includes acid sensitive side chains which can undergo
catalytic cleavage in the presence of an acid generated by the inventive
PAG. In such a polymer, the acid sensitivity exists because of the
presence of acid sensitive side chains that are bonded to the polymer
backbone. Such acid sensitive polymers including acid sensitive side
chains are conventional and are well known in the art. Preferably, the
imaging polymer is one suitable for use in 193 nm (ArF) lithography.

[0059] In some embodiments, the acid sensitive side chains of the acid
sensitive polymers are protected with various acid labile protecting
groups that are well known to those skilled in the art. For example, the
acid sensitive side chains may be protected with high activation energy
protecting groups such as t-butyl ester or t-butyl carbonyl groups, a low
activation energy protecting group such as acetal, ketal, or silyethers,
or a combination of both low and high activation energy protecting groups
may also be used.

[0061] Preferred imaging polymers contain at least about 5 mole % of
lactone-containing monomeric units based on the total monomeric units in
the imaging polymer, more preferably about 10-50 mole %, most preferably
about 15-35 mole %.

[0062] The photoresist compositions of the invention preferably contain a
solvent which is capable of dissolving the acid sensitive imaging
polymer. Examples of such solvents include, but are not limited to:
ethers, glycol ethers, aromatic hydrocarbons, ketones, esters and the
like. A solvent system including a mixture of the aforementioned solvents
is also contemplated herein. Suitable glycol ethers include:
2-methoxyethyl ether (diglyme), ethylene glycol monomethyl ether,
propylene glycol monomethyl ether, propylene glycol monomethylether
acetate (PGMEA) and the like. Suitable aromatic hydrocarbon solvents that
include: toluene, xylene, and benzene. Examples of ketones include:
methylisobutylketone, 2-heptanone, cycloheptanone, and cyclohexanone. An
example of an ether solvent is tetrahydrofuran, whereas ethyl lactate and
ethoxy ethyl propionate are examples of ester solvents that may be
employed herein.

[0063] In addition to the above components, the photoresist composition
may also include other components such as photosensitizers, bases,
surfactants or other additives. If desired, combinations or mixtures of
these other components may be used (e.g., a photosensitizer and a base).

[0064] The optional photosensitizer is preferably one containing
chromophores that are capable of absorbing irradiation in 193 nm (ArF)
lithography. Illustrative examples of such compounds include, but are not
limited to: 9-anthracene methanol, coumarins, 9,10-bis(trimethoxysily
ethynyl) anthracene and polymers containing these chromophores.

[0065] The optional bases that can be employed in the present invention
include, but are not limited to: aliphatic amines, aromatic amines,
carboxylates, hydroxides, or combinations thereof and the like.

[0066] The optional surfactants that can be employed in the photoresist
compositions include any surfactant that is capable of improving the
coating homogeneity of the chemically amplified photoresist composition
of the present invention. Illustrative examples include:
fluorine-containing surfactants such as 3M's FC-430® and
siloxane-containing surfactants such as Union Carbide's Silwet®
series.

[0067] The photoresist compositions of the invention preferably comprise
from about 1 to about 30 weight % imaging polymer, from about 50 to about
95 weight % solvent, and from about 0.1 to about 20 weight %
fluorine-free PAG (the weight % of the fluorine-free PAG is based on the
total weight of imaging polymer present in the composition).

[0068] When a photosensitizer is employed, it is preferably present in an
amount of from about 0.001 to about 8 weight %, based on the total weight
of imaging polymer. If a base is employed, the optional base is
preferably present in an amount of from about 0.1 to about 5 weight %,
based on the total weight of imaging polymer. When a surfactant is
employed, it is preferably present in amount of from about 0.001 to about
0.1 weight %, based on the total weight of imaging polymer.

[0069] More preferably, the photoresist composition comprises from about 5
to about 20 weight % of imaging polymer, from about 80 to about 95 weight
% solvent, and from about 0.5 to about 15 weight % of fluorine-free
photoacid generator (based on the total weight of imaging polymer present
in the composition), optionally, from about 0.01 to about 5 weight %
photosensitizer, based on the total weight of imaging polymer,
optionally, from about 0.1 to about 3 weight % base, based on the total
weight of imaging polymer, and optionally, from about 0.001 to about 0.01
weight % surfactant, based on the total weight of imaging polymer.

[0070] Note that the amounts given above are exemplary and that other
amounts of each of the above components, which are typically employed in
the photolithography industry, can also be employed herein.

[0071] The present invention also encompasses a method of using the
photoresist compositions of the invention to form patterned material
features on a substrate. Such a method includes: [0072] (a) providing a
material layer on a substrate; [0073] (b) forming a photoresist layer
over the material layer, the photoresist comprising: [0074] (i) an acid
sensitive imaging polymer; and [0075] (ii) a fluorine-free photoacid
generator comprising an onium cationic component and an anionic component
one of the following two structures:

[0075] ##STR00012## [0076] wherein: [0077] X is selected from the
group consisting of S, O and NR; [0078] R is selected from the group
consisting of H; linear, branched, tertiary, or cyclic alkyl; linear,
branched, tertiary or cyclic alkoxyl; unsubstituted and substituted
aromatic groups; and unsubstituted and substituted heteroaromatic groups;
[0079] Y is selected from the group consisting of C and N; and each of
G1-G5 is selected from the group consisting of R and an
electron withdrawing moiety, provided that when Y is N, G1 is not
present in the structure and at least one of G1-G5 is an
electron withdrawing moiety; [0080] (c) patternwise exposing the
photoresist layer to radiation, thereby creating a pattern of
radiation-exposed regions in the photoresist layer; [0081] (d)
selectively removing portions of the photoresist layer to expose portions
of the material layer; and [0082] (e) etching or ion implanting the
exposed portions of the material layer, thereby forming the patterned
material feature.

[0083] The substrate in the present invention is suitably any substrate
conventionally used in processes involving photoresists. For example, the
substrate can be silicon, silicon oxide, aluminum-aluminum oxide, gallium
arsenide, ceramic, quartz, copper or any combination thereof, including
multilayers. The substrate can include one or more semiconductor layers
or structures and can include active or operable portions of
semiconductor devices. The material layer may be a metal conductor layer,
a ceramic insulator layer, a semiconductor layer or other material
depending on the stage of the manufacture process and the desired
material set for the end product. The photoresist compositions of the
invention are especially useful for lithographic processes used in the
manufacture of integrated circuits on semiconductor substrates. The
photoresist compositions of the invention can be used in lithographic
processes to create patterned material layer structures such as metal
wiring lines, holes for contacts or vias, insulation sections (e.g.,
damascene trenches or shallow trench isolation), trenches for capacitor
structures, ion implanted semiconductor structures for transistors, etc.
as might be used in integrated circuit devices.

[0084] In some cases, a bottom antireflective coating and/or underlayer
coating (e.g., a planarizing underlayer) may be applied between the
photoresist layer and the material layer. In other cases, a top
antireflective coating layer may be applied over the photoresist layer.
The invention is not limited to the use of antireflective reflective
coatings and/or underlayer materials, nor specific compositions of those
coatings or materials.

[0085] The photoresist layer may be formed by virtually any standard means
including spin coating. The photoresist layer may be baked (post applying
bake (PAB)) to remove any solvent from the photoresist and improve the
coherence of the photoresist layer. The preferred range of the PAB
temperature for the photoresist layer is from about 70° C. to
about 150° C., more preferably from about 90° C. to about
130° C. The preferred range of thickness of the first layer is
from about 20 nm to about 400 nm, more preferably from about 50 nm to
about 300 nm.

[0086] The photoresist layer is then patternwise exposed to the desired
radiation. The radiation employed in the present invention can be visible
light, ultraviolet (UV), extreme ultraviolet (EUV) and electron beam
(E-beam). It is preferred that the imaging wavelength of the radiation is
about 248 nm, 193 nm or 13 nm. It is more preferred that the imaging
wavelength of the radiation is about 193 nm (ArF laser). The patternwise
exposure is conducted through a mask which is placed over the photoresist
layer.

[0087] After the desired patternwise exposure, the photoresist layer is
typically baked (post exposure bake (PEB)) to further complete the
acid-catalyzed reaction and to enhance the contrast of the exposed
pattern. The preferred range of the PEB temperature is from about
70° C. to about 120° C., more preferably from about
90° C. to about 110° C. In some instances, it is possible
to avoid the PEB step since for certain chemistries, such as acetal and
ketal chemistries, deprotection of the resist polymer proceeds at room
temperature. The post-exposure bake is preferably conducted for about 30
seconds to 5 minutes.

[0088] After PEB, if any, the photoresist structure with the desired
pattern is obtained (developed) by contacting the photoresist layer with
an aqueous alkaline solution which selectively dissolves the areas of the
photoresist which were exposed to radiation in the case of a positive
photoresist (or the unexposed areas in the case of a negative
photoresist). Preferred aqueous alkaline solutions (developers) are
aqueous solutions of tetramethyl ammonium hydroxide (TMAH). The resulting
lithographic structure on the substrate is then typically dried to remove
any remaining developer. If a top antireflective coating has been used,
it is preferably also dissolved by the developer in this step.

[0089] The pattern from the photoresist structure may then be transferred
to the exposed portions of underlying material layer of the substrate by
etching with a suitable etchant using techniques known in the art;
preferably the transfer is done by reactive ion etching or by wet
etching. Once the desired pattern transfer has taken place, any remaining
photoresist may be removed using conventional stripping techniques.
Alternatively, the pattern may be transferred by ion implantation to form
a pattern of ion implanted material.

[0090] Examples of general lithographic processes where the composition of
the invention may be useful are disclosed in U.S. Pat. Nos. 4,855,017;
5,362,663; 5,429,710; 5,562,801; 5,618,751; 5,744,376; 5,801,094;
5,821,469 and 5,948,570. Other examples of pattern transfer processes are
described in Chapters 12 and 13 of "Semiconductor Lithography,
Principles, Practices, and Materials" by Wayne Moreau, Plenum Press,
(1988). It should be understood that the invention is not limited to any
specific lithography technique or device structure.

[0091] The invention is further described by the examples below. The
invention is not limited to the specific details of the examples.

EXAMPLES

Example 1

Synthesis of mono nitro-benzo[b]thiophene-2-sulfonyl chloride

[0092] To a solution of benzo[b]thiophene-2-sulfonyl chloride (1.165 g, 5
mmol) in 25 mL of dichloromethane was added 3.6 mL of concentrated nitric
acid (>22.05 mol/L) dropwise, the resulting mixture was refluxed
overnight and cooled to room temperature before it was poured into 20
gram of crushed ice. The organic layer was separated and the aqueous
layer was extracted by 220 mL 2 dichloromethane. The organic layers were
combined and dried over MgSO4. Solvent was then removed by rotary
evaporator. The crude product was purified by flash column chromatography
with an eluent of hexane, followed by a gradient eluent of hexane/ethyl
acetate (6/1-3/1) to afford 0.58 g of product (mixture of 65% of
4-nitro-benzo[b]thiophene-2-sulfonyl chloride and 35% of
7-nitro-benzo[b]thiophene-2-sulfonyl chloride).

Example 2

Synthesis of silver mono nitro-benzo[b]thiophene-2-sulfonate

[0093] To a solution of mono nitro-benzothiophene-2-sulfonate (0.5177 g,
1.86 mmol) in 50 mL of acetonitrile and 1 mL of water was added silver
carbonate (0.6169 g, 2.24 mmol) in portions in darkness. The resulting
suspension was stirred overnight for 9 days, until no starting material
is shown on the thin layer chromatography with an eluent of hexane/ethyl
acetate (1:4). The mixture was filtered through half an inch of
Celite® and the solid was washed with 3×40 mL acetonitrile. The
organic filtrate was combined and organic solvent was removed via rotary
evaporator to dryness and thus afforded 0.668 g of viscous solid with a
yield of 98.2%. The resulting compound was not purified for further
reactions.

[0094] To a solution of silver mono nitro-benzo[b]thiophene-2-sulfonate
(0.668 g, 0.1.83 mmol) in 80 mL of acetonitrile and 4 mL of water was
added a solution of triphenyl sulfonium bromide (0.6271 g, 1.83 mmol) in
35 mL of acetonitrile and 1 mL of water. The resulting mixture was
stirred overnight for 3 days before it was filtered. The resulting
solution was filtered though 1 inch of Celite®/aluminum oxide
basic/Celite® layer and washed with 25 mL of acetonitrile and 25 mL
of acetone. The organic solvent was removed via rotary evaporator and the
residue was re-dissolved in 50 mL of 2-butanone, dried over magnesium
sulfate over night and filtered though 1 inch of Celite®. Solvent was
removed by rotary evaporator and dried over vacuum oven to dryness and
thus afforded 0.71 g of product with a yield of 70%. A melting point of
243° C. was obtained with TPSTBNO in a DSC measurement (10°
C./min, nitrogen 5 mL/min). No obvious decomposition up to 250° C.
was observed in the DSC measurement.

[0100] Thin solid films were prepared by spin-coating photoresist
formulations over 5 inch silicon wafers at the spin rate of 1500 rpm for
30 seconds. The resulting films were soft baked at 110° C. for 60
seconds. The thickness, n and k were measured by VASE ellipsometry, OD
values were calculated from k.

[0102] For lithographic evaluation, the prepared photoresists formulation
was spin-coated for 30 seconds onto an antireflective coating material
layer applied on silicon wafers. In the case of 193 nm immersion
lithography, a topcoat layer was applied above photoresist layer. The
resist film was baked at 11° C. for 60 seconds on a hotplate for
60 seconds. The wafers were then exposed to 193 nm radiation (ASML,
scanner 0.75 NA, and ASML, immersion scanner 1.35 NA, respectively). The
exposure pattern was an array of lines and spaces of various dimensions
down to 50 nm. The exposed wafer was then post-exposure baked on a hot
plate at 12° C. for 60 seconds. The wafers were puddle developed
by 0.263 N TMAH developer for 60 seconds. The resulting patterns of the
photoresist imaging layers were examined by scanning electron microscopy
(SEM). The photospeed results were obtained from the images of 150 nm
line/150 nm space and 50 nm line/50 nm space, respectively.

[0103] While the present invention has been particularly shown and
described with respect to preferred embodiments, it will be understood by
those skilled in the art that the foregoing and other changes in forms
and details may be made without departing from the spirit and scope of
the invention. It is therefore intended that the present invention not be
limited to the exact forms and details described and illustrated but fall
within the scope of the appended claims.